Particulate matter pollution in air poses a serious health threat and is responsible for thousands of deaths annually. Among particular matter particles, PM 2.5 mainly causes more morbidity and mortality worldwide after prolonged exposures, owing to their small particle size which can penetrate human bronchi and lungs compared to other larger size particulate matter resulting in lung disease, emphysema and lung cancer, especially in susceptible individuals and those suffering from respiratory and heart disease as their condition may be worsened by these particulate matter.
There are several filtration devices and systems currently in use. For example, modern commercial buildings have protection through filtering in ventilation systems which run on electricity and are often too noisy and even produce poisonous ozone gas. Individual safety masks like commercial respirators are commonly used as outdoor protection, which though prevent particle entry, make breathing difficult. Other common devices include air cleaning devices such as electrostatic precipitators and media filters which can be fitted to regulate particulate levels in buildings with central air conditioning systems. However, these devices are expensive and often not affordable to most housing societies. The existing air filter technology also has several shortcomings as most air purifiers are noisy and require filters to be replaced frequently. Further, ionizing air purifiers generate hazardous by-products like ozone gas which potentially causes respiratory ailments.
Recently, there has been a focus on developing nanofibrous materials for air filtration. A fibrous filter is comprised of a large number of randomly oriented fibers which form a dense material or mat which captures and retains particles throughout the depth or thickness. It is the thickness, fiber diameter, and density of the mat that enable fibrous filters to function. One such fibrous filter known in the art comprises advanced nanostructured carbon nanotube (CNT) structures, such as CNT/quartz-fiber nanotubes (CNTs). However, these are toxic. In another approach, several polymeric nanofibers, such as polyvinyl alcohol and poly-acrylonitrile with or without incorporation of nanoparticles, have been used and have shown good filtration efficiencies. However, the instability of nanoparticles over nanofibers is a concern. The nanofibers employed for air filters have been made by electrospinning, a process that utilizes an electric field applied to a drop of polymer melt or solution on the tip of the nozzle such that the droplet deforms and a charged jet accelerates toward the target, thereby generating nanofibers. However, the drawbacks of this technique are that it requires specialized equipment, high voltages, and electrically conductive targets and also suffers from a low deposition rate. Further, the diameters of electrospun fibers are much larger than the mean free path of air molecules and the mechanical properties of the electrospun fibers are not strong enough to be used in air filtration.
There is therefore a need for an improved nanofibrous filter for use in air filtration.